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Hortiscope

Ron Smith answers questions about the world of plants, trees and gardens.

By Ron Smith, Horticulturist

NDSU Extension Service

Q: We live in southeastern South Dakota. We have four apricot trees, but this is the first year they have produced fruit. We are wondering when to expect the fruit to be fully ripe for picking. (e-mail reference)

A: This is almost like asking when you realized that you had fallen in love. When the fruit looks ripe, but still firm, not soft, is the best time. The fruit will ripen after that at room temperature in a brown paper bag if you want to accelerate the process. If you want to drag the process out for a couple of days, allow the fruit to sit out in the kitchen. Enjoy!

Q: My problem is ants and more ants! I have anthills all over the yard. We have about 4 inches of black dirt in the yard. Under the black dirt are sand, gravel and rocks. I have tried Malathion and Sevin. I do have to admit that the Malathion is old. I have sprayed several times, but the ants are back a day or two later. What is the best pesticide to use and how often do I apply it? So far, the ants are not in the house. (Detroit Lakes, Minn.)

A: Forget commercial insecticides. Make up a soapy solution of garlic or tobacco juice and pour it into their holes. A synthetic insecticide on the market that is safe and effective is permethrin. Another solution is to mix boric acid (borate) with sugar and sprinkle it around the nests. They will pick it up and that will be the end of them. Sprays are more of an annoyance to ants than effective, so give it up and be thankful we don't have fire ants in this part of the country!

Q: We live in South Dakota. We had an old rhubarb patch that was overgrown with grass, so I dug up all the plants and moved them to a new location. They are now in a place closer to the house where we can keep the weeds and grass out. We never picked any last year or this year because we heard we were supposed to let it go two years before picking. Now the rhubarb is getting blight marks on the leaves. After that, the whole leaf turns orange and the stalk dies. What is wrong with our rhubarb and how can we help it? It seems to affect the green-stalked rhubarb worse than the old, red-stalked Russian rhubarb. (e-mail reference)

A: It sounds like a rust fungus might have moved in. I would suggest getting in touch with the South Dakota State University plant diagnostic lab at http://plantsci.sdstate.edu/planthealth/subpage.cfm?ID=12. I'm certain you will be asked for a sample of what you are talking about to be sure of the diagnosis.

Q: I have suckers coming from the base of my maple tree. I did buy Sucker-Stopper RTU, but need some clarification on its use. Do I prune off the suckers and then apply it or apply while they are still connected? Also, I have a Russian olive I keep severely pruned for use as an ornamental tree. There are many suckers that come out along each branch and seem to return as fast as I remove them. Can I spray Sucker-Stopper RTU on the branches? (e-mail reference)

A: Cut off the suckers and then spray the area or surface that you just cut. Same thing goes for the suckers on the branches.

Q: I am looking for a short crabapple to plant under a power line in a narrow space between an alley and driveway. I am thinking of spring bride crabapple. Is this plant available in the industry? Any other suggestions for a crabapple? (e-mail reference)

A: That is a tough space to fit crabapple trees. I don't know anything about spring bride crabapple. You might look into centurion crabapple because it tends to be more upright and is a hardy selection.

Q: I took a low corner in my yard and tried to establish a garden. It has not worked out, so I am looking at planting something more permanent, such as raspberries or some type of fruit. The spot I picked has good grass during the drier years, but is wet now. I was told there used to be a spring there prior to building houses and adding fill. I thought the spring would provide good
water, but the only thing that grows well is sunflowers. I have not had the soil tested, but I am positive that salt accumulation is the problem. Other than barley and sunflowers, are there any plants, fruit trees or shrubs that would do well in this soil? Would birch trees work? (e-mail reference)

A: Birch trees do well in damp, but not soggy soil. I would encourage you to get a soluble salt reading on that particular site before going to the expense and effort of planting anything.

Q: Should we cut the old blossoms off some Japanese tree lilacs now that they are done blooming? (e-mail reference)

A: Yes because it will help concentrate the energy for new growth and better flowering next year.

Q: I have about 10 plain cottonwood trees along my driveway. This year, I noticed some green pods in place of 25 percent to 40 percent of the leaves. I broke open a pod and found it was full of white bugs about the size of aphids. What should I do? (e-mail reference)

A: This is one of the many galls that inhabit cottonwood trees. Spraying now will do little good. Use insecticides next spring as the leaves are unfolding because that is when the adult lays her eggs in the opening buds.

Q: I have a question about rabbits. I used to raise them as a child, but never have heard of this before. I also talked to my parents and they had never heard of rabbits doing this, either. My son and his wife live in south Fargo. They think rabbits are eating and/or chewing at the bottom of the wood siding on their home. Do rabbits do this? Thank you so much. (e-mail reference)

A: I doubt that rabbits are the problem. It is more likely that squirrels are the problem. Whatever it is causing the problem, hot pepper spray around the area where they are chewing will bring that habit to a quick halt!

Q: Several years ago, I planted three batches of irises I received from my mother. I have one row of yellow irises and lavender iris plants on either side. This year, I noticed that the plants have developed huge seedpods. What I can't seem to find out is whether these pods are favorable. Have the plants cross-pollinated? If so, will they choke out my original plants? What do I do with the pods? Do I dispose of them or just take a wait-and-see approach? My mom says her plants never developed pods. (e-mail reference)

A: I would cut the pods out just in case the plants drop the seed and germinate. This could compromise your color scheme and plant vigor.

Q: I purchased two flats of marigolds. Unfortunately, I did not get them in the ground right away. Now they are dried up, except the bottom portion and the roots. A friend of mine who owned a nursery suggested I clip the tops and plant them anyway. Will the plants flower this summer or should I just say, “oh well, my mistake”? (e-mail reference)

A: It depends on how stubborn or experimental you are. I can’t tell you they will come back without seeing just what kind of condition they are in. I would trust your nursery friend and follow his advice because he has seen the plants.

Q: I have a question about boulevard trees. I looked at some tree species and am wondering if a cathedral or triumph elm would be a good choice to plant. Both are supposed to be Dutch elm disease resistant or do you discourage the planting of elms? I haven't found a honeylocust in any of our local greenhouses. I read that their larger branches tend to break in windstorms, which we are quite noted for, so I hesitate to plant that species. I also am looking at a variety of lindens. (Kulm, N.D.)

A: Either elm would be resistant. While I don't discourage planting elm trees, I am not in favor of a wholesale sweep of the landscape being planted with them, either. As long as elms are not a common tree in your area, you should be OK.

Q: You mention applying a lime/sulfur mixture to help save trees from black knot fungus. We have many trees with black knot. Can you elaborate a little more on the lime/sulfur remedy? Where do I get these products and what is the success rate? (e-mail reference)

A: Lime/sulfur is applied during the dormant season before leafing out takes place. It acts as a surface sanitizer that temporarily arrests the fungus activity. As the leaves open and the weather warms, the fungus becomes active and easily spreads, so an application of a fungicide containing benomyl is recommended. Do a follow-up spray again in 10 to 14 days. Repeat the spraying with the benomyl product if the weather is fickle in the spring. The visible knots should be pruned out a good 4 to 6 inches below the infection. None of this is guaranteed to stop the spread of this contagion, but it should slow it up somewhat. Go to a local garden supply store for either of these materials. If you cannot find the lime/sulfur (because it is not a proprietary product), then go with the benomyl product for the pre- and post-leafing cycles.

Q: We have a flowering plum tree we inherited with the house we bought three years ago. What a beautiful sight we enjoy every spring when it blooms! However, this summer the plums are coming in, but they are so heavy they are causing the branches to droop and the tree looks horrible. Can we prune in the summer or should we just pick the plums off and see what happens? (e-mail reference)

A: If you can pick off the excess plums carefully, that would be better. Pruning now in your particular summer climate would open the door for disease organisms to move in and really cause problems. Some folks tie them up with clothesline or prop them up with wood stakes, but that is not something I recommend because I have seen more problems from that action than from the weighty fruit.

Q: We have an early blooming apple tree (zestar), but never have had a good crop of apples. We have tried pruning, assisting with pollination and extra watering, but nothing seems to help. This year, we got good pollination and had hundreds of tiny apples. However, during the last two weeks, the tree has dropped nearly three-fourths of its apples. Can you please give me any thoughts on this? I have cruised around the Internet looking for ideas, but with no luck. Thanks in advance. (e-mail reference)

A: This is nature's way of saying too much or too many. When a heavy fruit set takes place, the plant usually will drop anywhere from 25 percent to 30 percent of its crop. That way, all the tree's energy is not expended into fruit production and it will or should have some left over for the following year.

Q: I received an e-mail from a potential client who has a strange tale. I believe she considers it a paranormal occurrence. She took a picture of a blue spruce (what looks to me like a bush, not a tree) that is a shade of pink, maybe even a light brown. She stated that it was taken around July 4 of this year. We have had some unusual temperatures for this time of year in Indiana. The evening temperatures were in the 40s for most of June. The first few nights of July were chilly and rainy. Could the weather be a reason the plant is changing colors? I would like to give her a professional reason that her plant is changing color and convince her that this is not a paranormal occurrence. Since I do not have a green thumb of any kind, your assistance is most appreciated. (e-mail reference)

A: Color change in plant material can be brought about by fluctuations in air and/or soil temperature. Cold, wet soil can inhibit the uptake of some nutrients that will cause the foliage to change colors, but only temporarily. Most of the time, plants will pull out of this, assuming no damage has occurred to the roots. Sometimes what is expressed by the foliage is reflective of the root environment not being in the best of shape. If you need more than this quick answer, get back to me.

Q: We have just moved to a new home that has a beautiful, old poplar tree. However, the tree is losing leaves, so I am raking constantly. Is this usual? The leaves that are falling are yellow and spotty. (Chicago, Ill.)

A: This is normal for poplars. It gets worse when the weather is hot or droughty. I would suggest getting an International Society of Arboretum certified arborist to inspect the tree to be sure it is sound and not a potential hazard to your property.

Q: I'm wondering what, if anything, can be done about blackbirds nipping off buds and flowers on my marigolds. The birds clip the buds and flowers off and shred them in the yard. So far, I haven't had a single bloom. Thank you for any help you can offer. (e-mail reference)

A: Blackbirds must be the adolescents of the bird world! Try scare balloons to see if that works. Also, try hot pepper spray. If they get a dab of that on their tongues, they'll stop!

Readers: If you are interested in learning more about woody plant, fruit and vegetable research, then plan to attend the NDSU horticulture research field day on Saturday, Aug. 2, at the Absaraka Horticulture Research Farm. A walking tour begins at 10 a.m. Participants are asked to bring a sack lunch, but drinks will be provided. On the tour, participants will see NDSU tree and shrub selections and introductions; common and exotic species; dwarf conifers; and Juneberry, grape and vegetable research plots. The 80-acre farm includes the 35-acre Research Arboretum, plus additional plot research areas. Dale Herman, NDSU woody plant selection and introduction researcher; Harlene Hatterman-Valenti, NDSU high-value crop researcher; and other NDSU research associates will conduct the tours. Go through Absaraka to Cass County Road 5 (sign posted). Turn north (left) and go about three-fourths of a mile (sign posted). Turn east (right) on the field road and proceed one-half mile to the Horticulture Research Farm, which is bordered by trees.